Variable geometry diffuser control for jet engines



March 28,- 1961 J. E. TAYLOR 2,976,677

VARIABLE GEOMETRY DIFFUSER CONTROL FOR JET ENGINES Filed Oct. 20, 1954 f4 "3 J8 f@ f7 2! 2 38 24J l' w 3 l I' 35 9 f6 K 1I 36 1f 25 37 WZMW? @wfg @f/@M95 United States Patent VARIABLE GEOMETRY DIFFUSER CONTROL FOR JET ENGINES John E. Taylor, Cleveland, Ohio, assigner to Thompson Ramo Wooldridge Inc., a corporation of Ohio Filed Oct. 20, 1954, Ser. No. 463,531

2 Claims. (Cl. 60-35.6)

The present invention relates to controls for jet engines of airplanes and more particularly is concerned with the provision of a control for the air inlet of engines such as turbojet, turboprop, ramjet, pulsejet and other engines using a high velocity air intake.

With the advent of aircraft capable of traveling above the speed of sound, air ow problems have become increasingly complex. As those skilled in the art are aware, movement of a body through air at a velocity greater than the speed of sound causes the development of shock waves or compression fronts.

The presence of shock waves has an important elfect on the operation of such items as jet engines, or any other apparatus deriving its lsource of air from an air scoop or diffuser opening toward the front of the'plane-.

While it is possible through calculations and experimentation to develop an air inlet for jet engines or the like which is eicient in operation under operating conditions in which the relative velocity of the air entering the inlet is greater than Mach l, the speed of sound, nevertheless such designs are generally only satisfactory when a characteristic shock wave, lfor example a normal shock wave, is positioned at a particular design region relative to the inlet. In view of this limitation of design it is necessary, in order to assure eflicient operation of the air inlet over wide ranges of aircraft speed and climaticconditions, that a control means be provided for modifying the position of the shock wave when it moves away from the optimum design region and to return it thereto.

The present invention has provided a control device for a jet engine air inlet located either on the nose of the aircraft or Idownstream thereof which is capable of operation at points well above the speed of sound and,

has provided the necessary control for accurately positioning a shock wave in the air inlet. This control generally comprises a sensing means positioned adjacent the air inlet and sensitive to variations in air density. The sensing means then relays, through appropriate control circuits, a signal indicating substantially the exact position of the shock wave in the air inlet, to a control motor which in turn operates a central air inlet spike or other apparatus, such as for example a wedge shaped central body, hinged or iris shaped air inlet outer lips, axially movable, telescopically mounted outer lips, side mounted hot bleed openings, etc. to modify the geometry of the air inlet to properly position the shock wave.

The sensing device utilized in the present invention comprises a bar coated with radioactive material extending longitudinal to the air ilow and parallel to an electrically conductive-channel element. The radioactive material coating the rod causes an ionization of the space between the bar and the channel. Thisionization, which is the result of a collision with air molecules of particles such as alpha, beta and gamma particles emittedskilled in. the 'art from a consideration ofthe attachedV 2,976,677 Patented Mar. 28, 1961 rent ilow resulting fromthe applied voltage will depend upon the density of the air between the bar and the channel, the radioactive device may be utilized as a sensing apparatus capable of determining the position of a shock wave when the shock wave lies across the bar and channel elements.

It isptherefore an object of the present invention to provide a novel and simple air pressure-sensing apparatus.

Still another object of the present invention is to provide a novel control for the air inlet geometry of an internal combustion engine or the like.

Yet a Ifurther object of the present invention is to provide a satisfactory air inlet control for use at relative inlet velocities above Mach l.

Still a further object of the present invention is to provide a rugged yet simple sensing apparatus for determining the position of a shock wave.

A feature of the present invention is the application of radioactive materials to air pressure-sensing apparatus. Yet a further object of the present invention is to provide a completely automatic control system for the air inlet opening of an internal combustion engine or the like operating under a relative air inlet velocity greater than Mach 1 and which automatically modifies the geometry of the inlet to vary the position of a shock wave occurring under supersonic conditions, in accordance with a predetermined most etcient design position.

Still other. and further objects and features of the present'inventionwill at once become apparent' to those sheet. of drawings wherein a preferred embodiment of the present invention isshown by way of illustration only and, wherein:

K Figure, l is an elevational viewv in cross-section of an internal combustion, jet type engine incorporating the present invention;

Figure 2 is an enlarged detailed view of the sensing device Vtaken along the line II-Il of Figure l;

Figure 3 is an elevational view of the sensing device taken along the line III-III of Figure 2; and

- Figure ,4 is a cross-sectional view of the sensing apparatus of the present invention taken along the line IV-IV of Figure 3. v

"As shown on the drawings:

As illustrated in Figure l, the apparatus of the present` invention is shown in combination with a jet type engine generally indicated at v10, havingan outer housing shell 11, an air inlet opening 12 a compressor compartment 13, a fuel mixing and igniting section 14 and a burner chamber 15. These elements, thus far discussed, are conventional and it will be understood that the presentl invention may be utilized with engines or similar devices having substantially any conventional form. of

power development, as long as the development of such power requires an intake compressible uid such as atvaries with the position the shock pattern assumes in the inlet or diffuser. Since the positioning of the shock pattern varies with relative inlet air velocity, atmospheric conditions, and back-pressure conditions determined `by compressor operation, among other things, it is apparent that Ywhere a lixed air inlet is utilized, it can be efficient 1inV providing'maximum pressure recoveryand minimum additive drag vsirmtltaneously only in a very limited nums ber or" conditions and situations.

In order to provide a suitably adjustable air inlet, a reciprocably movable control spike 16 ispositioned centrally in the inlet 12. The spike 16 Vis splined Vto "th`e stationary housing 17 which is in turn rigidly secured to the shell 11 by means of radiating struts 18. The spike 16 may be reciprocated relative to the housing 17 by 'means of an electrical motor 19 and suitable reduction gearing which drives a worm 20 drivingly associated with a nut` 21 xedly secure-d to the spike 16. As may be appreciated, reciprocation of the spike l2 will cause the annular inlet 1'2 to vary in effective size and flow configuration and will alsoof course, modify Vthe positionof the oblique bow wave 22. Spike adjustment will likewise modify the position of the normal. -shock 23, moving it axially in the opposite direction of spike movement, as well as the air ow indicated at 24. Of these changes, the adjustment of the position ofthe normal shock wave 23 is ofV primary concern since operational eticiency is. greatly affected by its position. l v

The present invention provides a novel means for controlling the position o-f the spike 16 and hence the exact position of the normal shock 23 under varying atmospheric and ight conditions. In so doing, I have provided a sensing mechanism automatically operable to determine the position of the normal shock by means of the sharp pressure rise across shock wave. The sensing mechanism` is connected through a suitable control network to the electric motor i9 to move spike 16 when necessary to reposition the shock wave into its most efficient position subsequent to a deviation therefrom as a result rof engine operating conditions. Y l

The sensing apparatus is more clearly illustrated in Figs. t2, 3 and 4. There, the sensing mechanism, generally indicated at 25 is shown to comprisea longitudinally extending electrically conductive channel'member 26 and a longitudinally extending electrically conductive member 27 positioned within the Vchannel and separated therefrom by insulated separators 28, 29 and 32. ln order to improve the aerodynamic characteristics of thesensing mechanism, theV separator29 is preferably formed with a sharp nose. This minimizes turbulence which would otherwisehave a deleterious elfect on .the accuracy of the sensing mechanism by causing unstable vpressure conditions. l

'The sensing mechanism -25 operates to control the flow of electricity in a circuit in response to Vthe density of air between the elements 26 and V27. V.In the .apparatus shown in the drawnigs, this is accomplished through coating the elongated member 27 with radioactive material 30 having suitable emission characteristics. For example, the element polonium may be satisfactorily used. v`This radioactive material emits alpha particles having a very high ionizing power because of their high mass to charge ratio. `It will be understood, however,.that the present invention is not limited to the use of polonium and that the rapid development of radioisotopes promiesto provide a large number of radioactive substances having satisfactory emission characteristics. t

Emission of the alpha'particles and their impact upon the air inthe space 31 betweenthe members 26 and 27 causes an ionization of the 'space `between the members 26 and 27. AA11 application of a voltageacross the elements 26 and'27 will 'cause' a current `flow across 'the ionized .air space. This current has 'been found to bear a linear relationship'to theaver'age density ofthe intervening air. Thus, assuming that anorm'al shock,"form ing an abrupt change ,in pressure, 'crosses the'mernbers 26 and 27 at some point intermediate theirilength, the

ly higher-density. lSince the average value ,of'thedensity l increase as the shock positions itself further upstream,

and likewise will decrease as the shock positions itself downstream relative to the sensing mechanism 25, the mechanism I25 can readily be utilized to sense the exact position of the shock Wave.

Since changing of the average density of the air space 31 will also occur as a result of changes in altitude, changes in air speed and changes in airtemperature, means must be provided for compensating lfor these variables. In the present invention a reference transducer, preferabiy substantially identical to the shock position sensing mechanism '25 lis positioned downstream of the air flow inthe air inlet chamber in -a position entirely Within the vhigh pressure zone .downstream of the normal shock. Alternatively, the rcferencetransducer may be positioned externally of the shell 11 at a point completely on ythe upstream side of the normal shock wave 23. Such a reference transducer is subject to all of the. variations except the variations imposed by the position of the shockwave itself and by balancing the current iiow from the reference transducer against the current ow of the shock Wave sensing mechanism when thek shock is in its desired position a resultant current reflecting only the variations in density occurring as a result of shock position, will be provided when the shock wave deviates from the desired position.

It is important, also, in the present invention wherein the shock position sensing mechanism utilizes a radioactive material, to provide compensation for disintegration ofl the radioactive material with time. This is particularly true incases where the radioactive material has a relatively 'short half life such as polonium vwith a half life "of 136 days. Inorder to ,provide the necessary com- 4,shock position 23. The connecting conductors 34, 35,V

[0 average densitywill befdetermined by the amount fof pensation, the reference transducer is preferably a radioactive one utilizing the same radioactive material.

j VSuc-l1A a reference transducer is shown at 33 inl the drawings and ispositioned well downstream of the normal 3'6 and 37 connect` the sensing mechanism and the reference transducer to the control box 38 where a .conventional bridge circuit is employed to provide a reversing actuation of the motor 19. The circuits employed may, of course, varyover a wide range but. preferably comprisea bridge circuit wherein the maximum current ilow in one direction is caused when substantially identical pressures are applied lto the reference transducer 33and the sensing mechanism 25. The maximum current iiow in the opposite direction, lto reverse theelectric motor, is Aachieved when the entire sensing Amechanism is .upstream of the shock Wave and hence at its lowest average air density, with the reference transducer wholly in the high pressure zone thereby providing a maximum pressure dierence.

the reference vtransducer 33 is,` along with a resistance adding rheostat, connected as one leg of the bridge .in parallel` with the sensingmechanism 25, any modification in the vresistance olered by the vsensing mechanism, as a resultof a variation in averagel pressure `between members 26 and 27 which is .not simultaneously also found inthe reference transducer resistance, will cause anunbalance inthe bridge causing energization of the motorr19-to'reciprocatethefspike 16 tomove the position of the shock wave 23 either upstream Yor downstream -as -requiredto place the bridge in balance again.

tIn operation, thesensing mechanism of the presentinvention is extremelyisatisfactory since itdoes not incorporateany coilwindings `Aor `similar elements that would The balanced point :at which it is de-` sired to place the normal shock preferably produces a disrupt air tlow through the jet engine. The coating 30 is, of course, preferably smooth and in view of the streamlined nature of the end insulating element 29, the air liow about the sensing mechanism is essentially streamlined flow. Further, although radioactive materials are at present relatively expensive, nevertheless in the quantities necessary to provide a current suiiicient to actuate the usual conventional motor relays, it has been found that less than $25.00 worth of polonium is suflicient to provide satisfactory operation for' at least a full half life of the material. In view of the simplicity of operation of the device and the minimum drag characteristics of the device placed in the air stream, the cost is quite nominal.

dit will ltherefore be appreciated that I have provided a simple and yet highly effective pressure sensing and control mechanism capable of sensing the position of a pressure discontinuity and which has an absolute minimum of physical eect on the air flowing past the sensing device. "Further, the sensing device is capable of simple manufacture and is usable with conventional current yamplifiers to provide a control signal suitable for the actuation of motor control relays of a conventional nature. In this last connection it is to be noted that while the motor 19 has been indicated to be an electric motor, it is apparent that hydraulic or pneumatic motor could be used equally as well, under the control of an electrically actuated valve controlling the source of motive power.

It will be understood that modification and variations may be made in the structure above described without departing from the scope of the novel concepts of the present invention. For example, it will be noted that the specific cross-section of the channel member 26 may be modified to assume an arcuate form, or, in some cases, it may take the form of a rod substantially the same as the rod 27, and extending parallel to the rod 27. Since such changes are considered within the scope of the -present invention, it is my intention that the invention be limited only by the scope of the appended claims.

I claim as my invention:

.1. Apparatus for sensing the position of an abrupt pressure change taking the form of a shock wave formed at the transition point of air slowing from a supersonic to a subsonic velocity while moving along a predetermined longitudinally etxending path, comprising a longitudinally extending member, a second member substantially parallel to said trst member in close proximity thereto, air streamlining cone means secured at the upstream ends of said rst and second members for smoothly deiiecting the air ow around said members, the space between said members permitting free transverse circulation between the members while said streamlining cone prevents substantial longitudinal movement of air between said members whereby the air between said members reliccts the average air pressure along the longitudinal length of said members without relation to its velocity, iirst means applying a voltage across said members and second means associated with said members for modifying the flow of current between said members in direct relation to the average density of the air between said members, said second means comprising an alpha particle emitting substance extending along the length of one of said members for ionizing the space between said members.

2v Apparatus for sensing the position of `an abrupt pressure change taking the form of a shock wave fonmed at the transition point of air slowing from a supersonic to a'subsonic velocity while moving along a predetermined longitudinally extending path, comprising a longitudinally extending member, a second member substantially parallel to said iirst member in close proximity thereto, air streamlining cone means secured at the upstream ends of said first and second members for smoothly deecting fthe air flow around said members, the space between said members permitting free transverse circulation between the members while 'said streamlining cone prevents substantial longitudinal movement of air between said members wheneby the air between said members reliects Athe average air pressure along the longitudinal length of said members without relation to its velocity, first means applying a voltage across said members and second means associated with said members for modifying the ilow of current between said members in direct relation to the average density of the air between said members, said second means comprising a radioactive coating on one of said members imposition thereon facing the other of said members and extending longitudinally the full length thereof for ionizing the air in the space between said tirst and second members.

References Cited in the le of this patent UNITED STATES PATENTS 2,462,351 Blau et al. IFeb. 2, 1949 2,497,213 Downing Feb. 14, 1950 2,637,208 Mellen May 5, 1953 2,638,738 Salter May 19, 1953 2,653,295 Carlson Sept. 22, 1953 2,627,543 Obermaier Feb. 3, 1953 

